Method and Device for Neural Implant Communication

ABSTRACT

Communications along a neural pathway are provided. The neural pathway is stimulated at a first location, in order to evoke neural responses which propagate along the neural pathway, the neural responses being modulated with data. At a second location spaced apart from the first location along the neural pathway the evoked neural responses are sensed. The sensed neural responses are then demodulated to retrieve the data. The stimulation could comprise peripheral sensory stimulation, and the second location could be at an implanted electrode array.

TECHNICAL FIELD

The present invention relates to implanted neural devices, being deviceswhich are able to evoke and/or sense neural activity upon a neuralpathway, and in particular to a method and system for establishingcommunication with such devices.

BACKGROUND OF THE INVENTION

A range of implanted neural devices exist, including: spinal cordimplants which electrically stimulate the spinal column in order tosuppress chronic pain; cochlear implants which electrically stimulatethe auditory nerve to produce a hearing sensation; deep brainstimulators which electrically stimulate selected regions of the brainto treat conditions such as Parkinson's disease or epilepsy; and neuralbypass devices which electrically stimulate either afferent sensorynerve fibres to reproduce impaired sensory function or efferent motornerve fibres to reproduce impaired motor activity, or both.

With the advent of high capacity implantable batteries andpower-efficient processing, implanted neural devices are becomingincreasingly complex and in particular numerous aspects of operation ofan implanted neural device may be reconfigurable. To control orreconfigure an implanted device thus requires the provision of acommunications channel from a controller outside the body to the devicewithin the body. Moreover, implanted neural devices are increasinglyserving a data gathering role, and there exists a need to provide acommunications channel from the device within the body to a data monitoroutside the body.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

In this specification, a statement that an element may be “at least oneof” a list of options is to be understood that the element may be anyone of the listed options, or may be any combination of two or more ofthe listed options.

SUMMARY OF THE INVENTION

According to a first aspect the present invention provides a method ofcommunicating along a neural pathway, the method comprising:

stimulating the neural pathway at a first location, in order to evokeneural responses which propagate along the neural pathway, the neuralresponses being modulated with data;

sensing the evoked neural responses at a second location spaced apartfrom the first location along the neural pathway, and

demodulating the sensed neural responses to retrieve the data.

According to a second aspect the present invention provides a method ofreceiving a communication from a neural pathway; the method comprising:

sensing on the neural pathway a plurality of evoked neural responses;and

demodulating the sensed evoked responses to extract data.

According to a third aspect the present invention provides a method oftransmitting information along a neural pathway, the method comprising:

evoking a plurality of neural responses on the neural pathway, theneural responses being modulated with data.

According to a fourth aspect the present invention provides animplantable device for communicating along a neural pathway, the devicecomprising:

sense electrodes and measurement circuitry for sensing neural responsespassing along the neural pathway; and

a processor configured to demodulate sensed neural responses to extractdata.

According to a fifth aspect the present invention provides anon-transitory computer readable medium for communicating along a neuralpathway, comprising instructions which, when executed by one or moreprocessors, causes performance of the following:

evoking a plurality of neural responses on the neural pathway, theneural responses being modulated with data.

The present invention thus utilises the neural pathway in a manner whichis distinguishable from natural neural signals in order to enable anartificial function, being communication to and/or from an implantedneural device. That is, rather than detecting neural responses which arenaturally arising, the present invention provides for the creation ofartificially occurring neural responses which carry a data payload orare otherwise artificially modulated for the purpose of communication,but which need not have any intended meaningful sensory or motorpurpose. The present invention thus utilises the neural pathway itselfas a communications channel. In contrast to other communicationstechniques, such as wireless communications or bulk tissue conductanceelectrical propagation, which require considerable electrical power toestablish the communications channel, the neural pathway does not needto be powered by the implanted device in order to function as acommunications channel, as the action potential is a biological functionrequiring no electrical power input after the neural response is firstevoked. That is, once evoked the action potential will continue topropagate for the full length of a healthy nerve without furtherexternal electrical power input.

The neural responses may be modulated with the data, such as being pulsewidth modulated, pulse amplitude modulated, pulse position modulated,amplitude or intensity modulated, delivered in bursts which arefrequency modulated, modulated by analog or digital modulation, or theymay be baseband on-off keying wherein presence of one or more neuralresponses within a given data bit window indicates a “1” and absence ofa neural response within the window indicates a zero, or vice versa. Thedata is to be understood as being machine readable data, as distinctfrom neural signals having a biological function such as being intendedfor the brain. For example the data may be binary data.

In accordance with various embodiments of the invention, the implantabledevice may be configured to only receive data via the neural pathway, orto only transmit data via the neural pathway, or both. The implantabledevice may further be configured to communicate by other means, such aswireless transmission when desired.

In some embodiments of the invention, the neural responses evoked forthe purposes of communication are configured to be comfortable for theimplant recipient. Indeed in some embodiments the neural responsesevoked for the purposes of communication may be configured to beminimally perceptible or wholly imperceptible by the implant recipient.Such embodiments recognise that certain low levels of neural activityare not perceived by the brain but can be selectively evoked by asuitable stimulator and detected by a suitable receiver. Suchembodiments may therefore be advantageous in avoiding the implantrecipient perceiving any, or any significant, aberrant effects fromcommunications stimuli. The perceptibility of the evoked communicationsresponses may additionally or alternatively be minimised by using veryshort-time stimuli for communications purposes and/or delivering stimuliin an interleaved manner with therapeutic stimuli so that thecommunications stimuli are not perceived or at least are not unpleasantto the user. It is to be noted that where neural responses are evoked bymotor activity such as the implant recipient activating a muscle, or bysensory input such as the user touching their leg, the neural responsesthereby evoked are perceptible but not typically uncomfortable and maynevertheless be modulated in order to effect communications along theneural pathway.

The step of stimulating the neural pathway may comprise stimulating thenerve directly, whether a spinal nerve, dorsal root ganglion orperipheral nerve. For example the nerve may be directly stimulated by anelectrical stimulus, an infrared or optical stimulus or a chemicalstimulus, in order to create neural responses modulated with data whichtravel to another site along the neural pathway for detection by aneural monitoring device.

Alternatively, the neural pathway may be indirectly evoked by deliveringa peripheral sensory input, such as a somatic touch or temperatureinput, or by proprioceptive activity such as may be caused by the useractivating or clenching one or more muscles or making one or moremotions in a particular predetermined manner which gives rise to neuralactivity which can be interpreted by a device monitoring the neuralpathway. Additionally or alternatively, the neural pathway may beindirectly evoked by delivering a visceral or parasympathetic sensoryinput in a particular predetermined manner which gives rise to neuralactivity which can be interpreted by a device monitoring an associatedneural pathway.

In some embodiments the communications may originate from an externalcontrol device, and may be configured to control or alter the operationof an implanted device. For example the external control device maydrive an input device such as a TENS device or a vibrational or hapticinput device, to deliver encoded peripheral sensory stimuli which giverise to neural responses modulated with data which propagate along theafferent sensory nerves to the implanted device. Such embodiments maypermit improved control of the duration, time and intensity of eachstimulus, and thus may be particularly suited to delivery of higher datarates to the implanted device as compared to manual sensory input.

In some embodiments, the vibrational device used to deliver sensoryinput to the neural pathway may be the mechanical vibrator of asmartphone. Such embodiments may be particularly advantageous inutilising a device already owned by many implant recipients, and whichhas considerable computing power and thus may be programmed to provideadvanced communications functionality with an implanted device byappropriately activating the mechanical vibrator for such communicationspurposes. The invention thus may be embodied in a smartphone app, whichfor example when executed controls a smartphone to communicate with animplant by vibrational sensory input.

Additionally or alternatively, in some embodiments the communicationsmay originate from manual human sensory input, such as from the implantrecipient. For example the communications originating from the implantrecipient may be configured to control or alter the operation of animplanted device. In some such embodiments the implant recipient maymanually deliver a sensory input to their peripheral nerves such as bytapping and/or stroking their leg(s) with their hand(s), in apredetermined pattern which gives rise to a pattern of neural responseswhich are detected and decoded by the implanted device. Additionally oralternatively, the communication may be initiated by motor input such asby the user clenching or activating one or more muscles or making one ormore motions in a predetermined manner which gives rise to neuralactivity which can be detected and decoded by the implanted devicemonitoring the neural pathway. Initiating communications via motoractivity rather than manual sensory input may be preferable if theimplant recipient is self-conscious about delivering peripheral sensoryinputs in public, as motor activity can be generated by activatingmuscles against resistance without requiring any movement and may thusbe more discreet. While embodiments utilising manual sensory input arelikely to achieve lower data rates than embodiments utilising anautomated stimulus method, manual sensory input is neverthelessadvantageous in permitting at least simple data input or device controlto take place without the need for any external control device.

The encoding or modulation scheme used for manual sensory inputcommunications is preferably configured to be distinguishable fromnormal motor activity, so that normal activity of the user is notundesirably detected as an instruction to change control settings of theimplanted device. For example, motor or proprioceptive activity may beencoded by requiring consecutive motor actions or sensory inputs on oneside of the body, so as to differentiate the encoded input from walkingin which motor or proprioceptive activity occurs on alternating sides ofthe body. Formulating appropriate encoded sensory or motor input for agiven implant recipient may be part of a fitting process afterimplantation of the implanted device. For example the user may have apreference of only tapping their feet to achieve such communications, orgently slapping their thighs, or the like. The user's preferred inputactivity may thus be accommodated during device fitting, in someembodiments. Moreover, the or each input pattern may resemble the rhythmof a favourite song or the like, to improve intuitiveness of the systemfor the user. In such embodiments the implanted device may thus beconfigured at the time of fitting to attach a unique control meaning towhichever input modulations are preferred by the user.

In further embodiments in which the communications originate from manualhuman input or a relocatable peripheral input such as a handheld TENSdevice, the implanted device may be configured to interpret such inputas having occurred at a location at which paraesthesia is required. Thismay occur during a temporary re-mapping mode which may be entered whenthe implant recipient or a clinician wishes to redefine deviceparameters in order to change a region of paraesthesia delivered by theimplanted device. When the device is in such a mode, an array ofelectrodes of the implanted device may detect neural responses on eachelectrode in a manner which corresponds to the indicated location of therequired paraesthesia. The device may then reconfigure a stimuluspattern in a manner that optimises the stimuli delivered from eachstimulus electrode, in a manner which optimally delivers paraesthesia tothe location defined by the sensory input. Electrodes to sense thelocation being indicated by the manual sensory input may be positionedadjacent to one or more dorsal root ganglion in order to ease thelocation mapping to within the corresponding dermatome. A similar effectmay be achieved by external device input such as by using an externalhaptic device to deliver sensory input at the location of requiredparaesthesia. Such embodiments may be particularly useful in cases ofinaccurate electrode array implantation during surgery, or post-surgicallead migration, to facilitate re-mapping of stimulus electrodes.

Additionally or alternatively, in some embodiments the communicationsmay originate from one implanted device which electrically stimulatesneural responses, and the evoked responses may propagate in either anefferent or afferent direction along the neural pathway to a secondimplanted device, in order to effect communications between twoimplanted devices. A communications network between a plurality ofimplanted devices may thus be achieved. The communication network maycomprise more than one neural pathway if data communicated along a firstneural pathway is transferred to a second neural pathway by a suitabledevice or devices.

Additionally or alternatively, in some embodiments the communicationsmay originate from an implanted device and may be configured topropagate to another location on the neural pathway to be detected anddecoded by a device external to the body, such as cranialelectrocardiography (ECG) electrodes configured to detect electricalneural activity or a surface electromyography (EMG) sensor configured todetect motor function such as a small muscle twitch or tic evoked byelectrical stimulus of motor fibres by the implanted device, within thecomfort range of the recipient, and modulated with data.

The communications delivered along the neural pathway may compriseinstructions to activate or deactivate a radio or other communicationscomponent of the implanted device. Such embodiments thus permit theradio component to be deactivated when not required to permit areduction in battery power consumption by the radio component, whilealso providing a means to reactivate the implanted radio, when requiredby a separate or external device or user.

The communications delivered along the neural pathway may compriseinstructions to activate, deactivate or alter a therapeutic function ofthe implanted device. For example when the user of a spinal cord implanttreating chronic pain intends to go to sleep they may instruct thedevice to turn off using communications in accordance with the presentinvention in order to save battery power overnight, and use equallysimple inputs to reactivate the therapeutic function when they wake up.

The implanted device is preferably operable to differentiate betweendistally evoked neural activity and locally evoked neural activity, forexample in the manner set forth in Australian Provisional PatentApplication No. 2014904595, also by the present applicant. Suchcapability may be important in embodiments such as spinal cord implantswhere the implanted device's therapeutic function involves substantiallycontinuous or ongoing locally evoked responses, from which distallyevoked responses which carry a communications purpose for the deviceneed to be differentiated.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 schematically illustrates an implanted spinal cord stimulator;

FIG. 2 is a block diagram of the implanted neurostimulator;

FIG. 3 is a schematic illustrating interaction of the implantedstimulator with a nerve;

FIG. 4 illustrates neural activity observed upon a neural pathway;

FIG. 5 illustrates modes of peripheral sensory data input to a neuraldevice in accordance with one embodiment of the present invention;

FIG. 6 illustrates a mode of peripheral sensory input to a neural devicein accordance with another embodiment of the present invention; and

FIG. 7 illustrates communication between two implanted neural devicesalong a neural pathway in accordance with another embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates an implanted spinal cord stimulator100. Stimulator 100 comprises an electronics module 110 implanted at asuitable location in the patient's lower abdominal area or posteriorsuperior gluteal region, and an electrode assembly 150 implanted withinthe epidural space and connected to the module 110 by a suitable lead.Numerous aspects of operation of implanted neural device 100 arereconfigurable by an external control device 192. Moreover, implantedneural device 100 serves a data gathering role, and gathered data needsto be communicated to external device 192. These functions of implanteddevice 100 thus require the provision of a communications channel 190from a controller 192 outside the body to the device 100 within thebody.

FIG. 2 is a block diagram of the implanted neurostimulator 100. Module110 contains a battery 112 and a telemetry module 114. In embodiments ofthe present invention, any suitable type of transcutaneouscommunication, such as infrared (IR), electromagnetic, capacitive andinductive transfer, may be used by telemetry module 114 to transferpower and/or data between an external device and the electronics module110.

Module controller 116 has an associated memory 118 storing patientsettings 120, control programs 122 and the like. Controller 116 controlsa pulse generator 124 to generate stimuli in the form of current pulsesin accordance with the patient settings 120 and control programs 122.Electrode selection module 126 switches the generated pulses to theappropriate electrode(s) of electrode array 150, for delivery of thecurrent pulse to the tissue surrounding the selected electrode.Measurement circuitry 128 is configured to capture measurements ofneural responses sensed at sense electrode(s) of the electrode array asselected by electrode selection module 126.

FIG. 3 is a schematic illustrating interaction of the implantedstimulator 100 with a nerve 180, in this case the spinal cord howeveralternative embodiments may be positioned adjacent any desired neuraltissue including a peripheral nerve, visceral nerve, parasympatheticnerve or a brain structure. Electrode selection module 126 selects astimulation electrode 2 of electrode array 150 to deliver an electricalcurrent pulse to surrounding tissue including nerve 180, and alsoselects a return electrode 4 of the array 150 for stimulus currentrecovery to maintain a zero net charge transfer.

Delivery of an appropriate stimulus to the nerve 180 evokes a neuralresponse comprising a compound action potential which will propagatealong the nerve 180 as illustrated, for therapeutic purposes which inthe case of spinal cord stimulator for chronic pain might be to createparaesthesia at a desired location.

The device 100 is further configured to sense the existence andintensity of compound action potentials (CAPs) propagating along nerve180, whether such CAPs are evoked by the stimulus from electrodes 2 and4, or otherwise evoked. Thus, communications originating elsewhere alongthe neural pathway and intended for the device 100, and comprising anencoded sequence of action potentials, may be sensed by the device 100.To this end, any electrodes of the array 150 may be selected by theelectrode selection module 126 to serve as measurement electrode 6 andmeasurement reference electrode 8. Signals sensed by the measurementelectrodes 6 and 8 are passed to measurement circuitry 128, which forexample may operate in accordance with the teachings of InternationalPatent Application Publication No. WO2012155183 by the presentapplicant, the content of which is incorporated herein by reference.

FIG. 4 is a plot of neural activity observed upon the spinal cord 180 bythe device 100. During the period shown, four minutes, the implantrecipient was asked to perform certain movements, as follows: nomovement at around 20-30 s, rubbing leg around 40-50s, lifting legaround 60-70s, and walking during the period 120-140 s. The presentinvention recognises that each active movement is distinguishable from alack of movement, and that each such sensory or proprioceptive input canbe deliberately modulated with data in order to communicate with theneural device 100.

FIG. 5 illustrates modes of peripheral sensory data input involving theuser tapping their feet and/or slapping their thighs. The user may knowto perform such activities in a predefined pattern which can bedistinguished in the neural signal as a communication, for example theuser may tap their feet in Morse code or to replicate a favourite song.The user may also or alternatively clench or activate certain muscle(s)to communicate with the SCS 100.

FIG. 6 illustrates machine-assisted sensory input to communicate withthe implanted device 100, in the form of a smartphone 600 configured todeliver vibrational sensory inputs to the user's thigh, to induceafferent sensory activity on the lateral femoral cutaneous nerve 602,for detection by the device 100. In this embodiment, communication ofexternal information or commands to the implanted system 100 is effectedby placing the vibration device 600 on an area of skin which isneurologically addressed by the electrode array 150. Externalinformation or commands are encoded as a sequence of vibrations, and thedevice 600 is controlled to vibrate according to that sequence. Theevoked sequence of neural stimuli then propagate afferently along nerve602 and into the spinal cord 180 and are then observed through theelectrodes 150. The observed neural response sequence is decoded by theimplant 110 to recover the original information or commands. Theencoding of the sequence of vibrations may be carried out in accordancewith any suitable encoding scheme such as being pulse width modulated,pulse amplitude modulated, pulse position modulated, amplitude orintensity modulated, delivered in bursts which are frequency modulated,modulated by analog or digital modulation, or on-off keying. Thisarrangement has the advantage that there is no need for the telemetrymodule 114 to be constantly active to receive radio communications.Instead, sensory input communications from device 600 may be used toselectively activate telemetry module 114 only when needed, or may beused for any other communications purpose.

Device 600 operates in this manner under the control of an app, and suchapps configured for communications with neural implants for therapeuticor other purposes are within the scope of the present invention.

The arrangement of FIG. 6 may additionally or alternatively be used tore-program a site of paraesthesia effected by device 100. In suchembodiments, the memory 118 is populated with a store of calibrationdata to assist in identifying the location where the skin is touched bydevice 600. The calibration data is produced as follows: (a) neuralresponses are measured by device 100 while touching specified locationson the skin, and (b) information is stored in the calibration storeindicating the nature of measurements which arise for each location.Then when re-programming of the site of paraesthesia is required, as maybe initiated by any suitable communications method including thosedescribed herein, a re-programming mode is entered in which the device600 is held against the skin at a location of desired paraesthesia, andcaused to deliver vibrational sensory inputs. The evoked neural activityis observed by device 100 and matched to the closest match(es) from thecalibration store in memory 118, and used to re-set the patient settings120 such as stimulus electrode selection.

FIG. 7 illustrates communication between two implanted devices 110 and710, along a neural pathway 180. Device 710 is a vagus nerve stimulatorwhich comprises an implanted electrode array 752 configured to stimulatethe vagus nerve 182 for therapeutic purposes such as treatment ofepilepsy or depression. Device 710 further comprises an electrode array750 implanted alongside the spinal cord 180 in order to enablecommunications with the device 110 along the communications channelprovided by the spinal cord 180. Device 110 may thereby communicate withdevice 710 by causing the delivery of encoded stimuli from electrodearray 150 to the spinal cord 180, in order to evoke neural responseswhich propagate along the spinal cord. Array 750 is then able to sensethe passing sequence of neural activity evoked by the device 110, fromwhich the device 710 decodes the communications. For example, device 110may be operable to monitor a heart rate of the patient by reference toheartbeat modulations of observed neural responses on the spinal cord180, and to communicate to device 710 at times when changed vagus nervestimulation is required in order to influence a heart rate of thepatient. The configuration of array 750 and the associated components ofdevice 710 may be substantially the same as for device 100 as shown inFIG. 3.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notlimiting or restrictive.

1. A method of communicating along a neural pathway, the methodcomprising: stimulating the neural pathway at a first location, in orderto evoke neural responses which propagate along the neural pathway, theneural responses being modulated with data; sensing the evoked neuralresponses at a second location spaced apart from the first locationalong the neural pathway, and demodulating the sensed neural responsesto retrieve the data.
 2. The method of claim 1 wherein the neuralresponses are modulated with the data by on-off keying.
 3. The method ofclaim 1 wherein the communicated data instructs a neural device toactivate a wireless transceiver.
 4. The method of claim 1 wherein theneural responses evoked for the purposes of communication are configuredto be minimally perceptible or imperceptible by the implant recipient.5. The method of claim 4 wherein perception of the evoked communicationsresponses is minimised by using short-time stimuli.
 6. The method ofclaim 4 wherein perception of the evoked communications responses isminimised by delivering stimuli in an interleaved manner withtherapeutic stimuli.
 7. The method of claim 1 wherein the modulatedneural responses are evoked by motor activity.
 8. The method of claim 1wherein the modulated neural responses are evoked by sensory input. 9.The method of claim 1 wherein the modulated neural responses are evokedby stimulating the neural pathway directly.
 10. The method of claim 1wherein the communications originate from an external control device,and the data are configured to control or alter the operation of animplanted device.
 11. The method of claim 10 wherein the externalcontrol device comprises a vibrational input device.
 12. The method ofclaim 11 wherein the vibrational input device is a mechanical vibratorof a smartphone.
 13. The method of claim 1, further comprisingformulating appropriate encoded sensory or motor input for a givenimplant recipient as part of a fitting process after implantation of theimplanted device.
 14. The method of claim 12 wherein the fitting processincludes configuring the implanted device to attach a unique controlmeaning to input modulations selected by the user.
 15. The method ofclaim 1 further comprising entering a temporary re-mapping mode toredefine device parameters in order to change a region of paraesthesiadelivered by the implanted device.
 16. The method of claim 1 , whereinthe communications originate from one implanted device whichelectrically stimulates neural responses, and wherein the evokedresponses propagate along the neural pathway to a second implanteddevice, in order to effect communications between two implanted devices.17. The method of claim 1, wherein the communications originate from animplanted device and propagate to another location on the neural pathwayto be detected and decoded by a device external to the body.
 18. Themethod of claim 1 wherein the communications delivered along the neuralpathway comprise instructions to activate, deactivate or alter atherapeutic function of the implanted device.
 19. The method of claim 1wherein the implanted device is operable to differentiate betweendistally evoked neural activity and locally evoked neural activity. 20.A method of receiving a communication from a neural pathway; the methodcomprising: sensing on the neural pathway a plurality of evoked neuralresponses; and demodulating the sensed evoked responses to extract data.21. A method of transmitting information along a neural pathway, themethod comprising: evoking a plurality of neural responses on the neuralpathway, the neural responses being modulated with data.
 22. Animplantable device for communicating along a neural pathway, the devicecomprising: sense electrodes and measurement circuitry for sensingneural responses passing along the neural pathway; and a processorconfigured to demodulate sensed neural responses to extract data.
 23. Anon-transitory computer readable medium for communicating along a neuralpathway, comprising instructions which, when executed by one or moreprocessors, causes performance of the following: evoking a plurality ofneural responses on the neural pathway, the neural responses beingmodulated with data.